The role of the properdin system in the activation of the complement system in these diseases and in rheumatoid arthritis will be investigated by studying tissue and serum from these patients. Properdin, Factor B, C3, C4, C2 will be studied in the serum and in tissues and correlated with various clinical parameters with the disease and with the presence of a variety of circulating antinuclear antibodies. Evidence for activation of the properdin pathway by nuclear antigens will be studied in vitro as will the possible activation of the properdin pathway by various antinuclear antibody-nuclear antigen complexes. The metabolism of C3, properdin and Factor B will be studied in patients with SLE and the results correlated with deposition of these proteins in kidney and skin and with their serum levels. The studies should lead to a better understanding of the pathogenesis of damage in connective tissue diseases.